GB657053A - Improvements in or relating to cathode ray tubes and signalling systems incorporating such tubes - Google Patents

Abstract

657,053. Automatic control systems for telegraphy. WESTERN ELECTRIC CO., Inc. July 25, 1947, No. 20134. Convention date, Oct. 7, 1942. [Class 38 (iv)] [Also in Groups XL (a) and XL (b)] A high-speed receiver for signals which are of constant frequency but differently phased impulses comprises a cathode-ray tube in which the beam scans, in synchronism with the signal frequency, a circle concentric with a number of targets to one of which the beam is momentarily reflected in accordance with the signal by concentric electrodes. A magnetic or optical record on wire or tape is used for modulating the carrier frequency. The receiver is shown in Fig. 3, and comprises a cathode-ray tube 300 provided with an electron gun 312, a magnetic focusing coil 313, a fluorescent screen 370 and a screen 340 on which are cut 32 stencil characters. The signals are fed to the detector 212 through the receiver 211 and the electron beam scans a circle which is concentric with, and is inside or outside the circle of stencils. The scanning plates 321, 322, the potentials on which are controlled in accordance with the carrier frequency, are connected through the sweep circuit 225, switch 224, amplifier 223, subharmonic generator 222, filter 221 to the detector D. Generators 90, Fig. 2, 228, Fig. 3, which are independent of the signalling frequency, may be used to control in synchronism both the speed of the transmitting film and the scanning plates 321, 322, Fig. 3, through switch 224, Fig. 3. The signalling impulses are supplied over lines 214 to the deflecting electrodes 330, 331 so that the beam is deflected radially across the appropriate stencil to reproduce the selected cipher on the screen 370. A further pair of radial deflecting plates causes the beam to strike the middle of the screen where the letters may read in succession or focused on to a moving photorecording tape (Fig. 3A, not shown). For printing in page form, deflecting plates 360 inside or outside the tube cause the characters to appear in a line on the screen. Each stencil 343, Fig. 6, is surrounded by a disc electrode 344 and associated with segmental electrodes 345, 346. In order to synchronize the receiver with the transmitter, the phase of the scanning beam with respect to the carrier frequency is adjusted by the knob 241, Fig. 3, on the starting circuit until the selected letter appears on the screen. The shaft of the knob may be fitted with an electromagnetic clutch so that when the beam impinges on the disc 344 surrounding the selected letter, an impulse through the line 347 to the starting circuit energizes the clutch to disconnect the knob. Finer adjustment is obtained by the electrodes 345, 346 one of which is hit by the deflected beam if the point of deflection is out of phase so that a correcting impulse is conveyed to the. synchronizing circuit 250. In a modification a synchronizing impulse may be recorded on the transmitter film and a corresponding target 236, Fig. 3, will replace electrodes 344, 345, 346, Fig. 6.